Submarine cables for power supply, telecommunications and the like can in the most cases not be laid down directly on the sea-bottom but has to be protected against, for example, floating ice, fishing-tackle, anchors and the like. The cable can either be covered with, for example, iron blocks and cement sacks or the cable can be brought down into the bottom material, for example, by digging and ploughing. The alternative of covering of the cable is mostly very expensive and time-wasting and this method has earlier been used only when it was considered necessary. For digging of cable trenches dredgers have been used. This method is expensive, technically difficult to master and limited to shallow waters. Apparatus for digging cable trenches and simultaneous laying of cable are previously known, for example in Swedish Patent No. 322,279. The known arrangements have, however, been intended to work in loose bottom materials such as sand, mud, soft clay and the like. The aim has principally also been to lay down weaker cables or water conduits in relatively calm waters inside a belt of islands. These arrangements are scarcely applicable for ocean operations, hard and rough bottom and heavy cable constructions as, for example, armoured power cables. Even arrangements for similar operations are previously known, with unsatisfying results in certain cases, among other things the difficulties have been great really to have the cable dug down.